How do a add new monitors to existing devices all at once

Hello

I need to find out how to add new monitors (CPU & Memory) to my existing devices. If I do a rediscovery of the current devices and choose the new monitors it will add the same server again instead of just assigning the new monitors to the existing servers.

I have about 900+ servers and to manually go to each one and select add new monitor is not an option

Please advise

Thanks